As the White House lobbies undecided lawmakers, House leaders say they are close to a majority on Obama's plan to fight global warming. Republicans and some industry groups intensify attacks.

WASHINGTON — House Democrats grew increasingly confident Thursday that they have the votes to deliver on one of President Obama's highest priorities -- a landmark effort to fight global warming and boost alternatives to fossil fuels.

With the vote coming as early as today, House leaders said they were closing in on majority support but had not locked it down yet.

"We're going to get the votes," said Rep. Edward J. Markey (D-Mass.), who co-wrote the bill with Rep. Henry A. Waxman (D-Beverly Hills). "We're going to pass the most important energy and environment bill in the history of the United States."

Passage of the bill would be a major victory for Obama at a time when the president's poll numbers have dropped slightly and his administration is juggling efforts to overhaul healthcare, reform financial regulations, and deal with Iran, North Korea and other foreign policy challenges.

Mindful of the stakes, Obama on Thursday deployed Chief of Staff Rahm Emanuel, top climate-change advisor Carol Browner and several Cabinet officials and key staff to lobby on-the-fence lawmakers -- in phone calls and face-to-face meetings and at a long-scheduled congressional luau at the White House.

The president also made several calls to undecided members. He appealed to others in a quick afternoon speech in the Rose Garden.

"I know this is going to be a close vote," Obama said, "in part because of the misinformation that's out there that suggests there's somehow a contradiction between investing in clean energy and our economic growth. But my call to those members of Congress who are still on the fence, as well as to the American people, is this: We cannot be afraid of the future, and we can't be prisoners of the past. . . . Now is the time to finally act."

A presidential phone call helped win at least one vote: Rep. Debbie Halvorson (D-Ill.), a freshman lawmaker and former state Senate colleague of Obama's, said Thursday evening that after months of indecision, she "feels great" about the bill.

"I think it's something that I'm going to support," Halvorson said. "It's a thousand-page bill. It has a lot of amendments. I wanted to read it, take my time." Later, she added: "I had a nice chat with the president this morning."

Faced with the increasing likelihood that Democratic leaders would bring the bill to a floor vote today, Republicans and some industry groups -- including the American Farm Bureau Federation, the U.S. Chamber of Commerce and the American Petroleum Institute -- intensified their attacks.

House Republican leader John A. Boehner of Ohio said the bill would create an unworkable government bureaucracy, and others continued to label it an "energy tax" and say it would harm American business.

The bill "is going to force small businesses and their workers and their families to pay more for electricity, gasoline and other products that are made in America that have a high energy content," said Rep. Howard P. "Buck" McKeon (R-Santa Clarita). "This will cause high-energy industries, like the steel-making industry, to move out of the United States and to our competitors such as China, India and South Korea."

The legislation is centered on a "cap-and-trade" system in an effort to limit the heat-trapping greenhouse gas emissions that scientists blame for global warming.

Under the system, major sources of those gases -- including factories and power plants -- would need to obtain permits for their emissions or buy "offsets" to cover them. The number of permits would fall every year, reducing emissions by more than 80% by 2050. Most emitters would initially get free permits, but in later years would buy them at auction.

House Speaker Nancy Pelosi (D-San Francisco) decided to push for a vote this week because she wanted to "seize the moment," Democratic aides said, sensing that support for the bill was fragile and delay could undermine the shifting consensus.

But as the vote neared, Democrats still were going their separate ways.

For example, Rep. Tom Perriello, who represents a rural but increasingly Democratic section of Virginia, said he would support the bill. Rep. Earl Pomeroy, a conservative Democrat from North Dakota, said he would vote against it, citing his fear that the bill would drive up energy prices and harm his state's coal industry.